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<td ><a href="../qtdoc/index.html">Qt 5.12</a></td><td ><a href="qtquick-index.html">Qt Quick</a></td><td >
			Qt Quick中的重要的概念 - 可视画布</td></tr></table><table class="buildversion"><tr>
<td id="buildversion" width="100%" align="right"><a href="qtquick-index.html">Qt 5.12.3 参考指南</a></td>
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<li class="level1"><a href="#coordinate-system"><span lang="zh-cn">坐标系统</span></a></li>
<li class="level1"><a href="#visual-parent"><span lang="zh-cn">可视父</span></a></li>
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<h1 class="title">Qt Quick中的重要的概念 - 可视画布</h1>
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<p>Qt Quick提供的可视化画布是一个具有z顺序的二维画布。</p>
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<h2 id="coordinate-system"><span lang="zh-cn">坐标系统</span></h2>
<p>在Qt Quick坐标系中，左上角像素为[0,0]像素。子项目的坐标系统是相对于它的可视父项目的。有关Qt Quick使用的坐标系统的详细信息，请参阅有关<a href="qtquick-visualcanvas-coordinates.html">坐标系统</a>的文档。</p>
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<h2 id="visual-parent"><span lang="zh-cn">可视父类</span></h2>
<p>在使用Qt Quick的QML应用程序中，有两种不同的父类方式。第一类是所有权父类(也称为<a href="../qtcore/qobject.html">QObject</a>父类)，它确定对象生命周期语义。第二种是可视父类，它决定了项目在画布上的绘制位置，以及某些属性(例如，不透明度应用于可视子类)。</p>
<p>在几乎所有情况下，可视父类都与所有权父类相同。有关该主题的更深入信息，请参阅有关<a href="qtquick-visualcanvas-visualparent.html"><span lang="zh-cn">可视父类</span></a>的文档。</p>
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<h2 id="scene-graph"><span lang="zh-cn">场景图</span></h2>
<p>现代计算机系统和设备使用图形处理单元或图形处理器来渲染图形。Qt Quick可以通过使用OpenGL之类的图形api来利用这些图形硬件。Qt 
Quick的默认图形适配需要OpenGL，它用于在QML中显示使用Qt Quick开发的应用程序。特别地，Qt 
Quick定义了一个场景图，然后进行渲染。有关场景图的概念、场景图的好处以及Qt Quick提供的<a href="qtquick-visualcanvas-scenegraph.html">场景图</a>适应性的深入信息，请参阅有关场景图的文档。</p>
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